Prior treatment (priming) with a subimmunogenic does of Type III pneumococcal polysaccharide (SSS-III) results in an antigen-specific T-cell dependent form of unresponsiveness (low-dose paralysis). Such unresponsiveness can be transferred by spleen cells obtained 5-24 hr after priming. The suppressive activity of transferred cells is abolished by prior treatment with monoclonal anti-Thy 1, anti-Lyt-2, and anti-I-J antibody in the present of complement; thus, suppression is mediated by a distinct subset of T cells (suppressor T cells). However, if primed spleen cells are transferred 24-72 hrs after immunization with SSS-III, the resulting antibody response of immunized recipients is enhanced, rather than suppressed. Greater enhancement is noted using transferred cells pretreated with monoclonal anti-Lyt2 antibody plus complement to remove suppressor T cells; such enhancement is attributed to amplifier T cells having the Lyt-1 phenotype. These findings indicate that suppressor T cells regulate the antibody response to SSS-III by influencing the expansion of SSS-III - specific clones of B cells as well as the expression of amplifier T cell activity; ther latter cause B cells to proliferate further in response to SSS-III.